Goodwill and intangible assets (Estimated Amortization Expense) (Details) - USD ($) $ in Millions	Sep. 30, 2022	Sep. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization expense next year	$ 59.7
Amortization expense year two	58.1
Amortization expense year three	58.0
Amortization expense year four	53.2
Amortization expense year five	51.6
Amortization expense thereafter	252.7
Net Carrying Amount	$ 533.3	$ 505.6